About the microdetermination of thallium with rhodamine B

Summary The spectrophotometric determination of thallium with Rhodamine B as Rhodamine B-thallium(III) tetrabromide using extraction of the complex into benzene was investigated. For the oxidation of thallium(I) ceric sulphate was used. The optimum conditions and interferences of some ions for the determination of microgram amounts of Tl are described. The sensitivity is 0.0028 g of Tl per 1 ml of benzene. 5 g of Tl can be determined with a precision of ±2.4%. The method described may be applied in trace analyses of thallium, where sulphuric-nitric acid is used for the decomposition of the sample.

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Zusammenfassung Ein spektrophotometrisches Verfahren zur Thalliumbestimmung mit Rhodamin B wird beschrieben, bei dem der gebildete Thallium(III)-komplex mit Benzol extrahiert wird. Zur Oxydation von einwertigem Thallium wird Cer(IV)-sulfat verwendet. Die optimalen Bedingungen sowie Störungen durch Fremdionen bei der Bestimmung von g-Mengen Thallium werden beschrieben. Die Empfindlichkeit betrÄgt 0,0028 g Tl/1 ml Benzol. 5 g Tl können mit einer Genauigkeit von±2,4% bestimmt werden. Das beschriebene Verfahren kann bei der Spurenanalyse von Thallium in solchen Proben benutzt werden, die mit Schwefel- und SalpetersÄure aufgeschlossen worden sind.

     

ANVAS: Artificial Neural Variables Adaptation System for descriptor selection

A new algorithm model-oriented for variable selection is presented in this study. It is based on the combination of genetic algorithms (GA) for hyperspace exploration, and counterpropagation artificial neural network (CP ANN) for deriving the fitness score. The proposed method performed very well on both well defined synthetic data sets and real academic data sets.     

Spectral representation of reduced protein models

We consider a spectrum-like two-dimensional graphical representation of proteins based on a reduced protein model in which 20 amino acids are grouped into five classes. This particular grouping of amino acids was suggested by Riddle and co-workers in 1997. The graphical representation is based on depicting sequentially the amino acids on five horizontal lines at equal separations. One-letter codes, B, O, U, X and Y, to which numerical values 1 to 5 have been assigned, are suggested as labels for the fictional amino acids that represent all the amino acids within each group. The approach is illustrated on ND6 proteins of eight species having from 168 to 175 amino acids. While visual inspection of the novel spectral graphical representations of proteins may reveal local similarities and dissimilarities of protein sequences, arithmetic manipulations of spectra offer an elegant route to graphic visualization of the degree of similarity for selected pairs of proteins.     

Determination of the oxygen balance in oxide superconductors by a photometric method

Summary A photometric method is described for determining the oxygen balance in oxide superconductors. It is based on the oxidation of Fe²⁺ to Fe³⁺ by the superconductors and the following determination of the residual Fe²⁺ ions as complex with 1,10-phenanthroline. Hydrobromic acid is used for dissolving the samples. The method has been developed for 10 mg sample weights. Good reliability of the method was verified by comparison with the cerimetric determination using 80 mg samples.     

Spektrographische Bestimmung der Verunreinigungen in Wolframs?ure

Zusammenfassung Es wird eine Methode zur quantitativen Bestimmung von Fe-, Al-, Mn und Mg-Spuren in Konzentrationen von 0,001–0,01% in Wolframsäure beschrieben. Die genannten Elemente werden gemeinsam mit einem kleinen Kupferzusatz, der als Kollektor und Eichelement dient, aus der ammoniakalischen Lösung durch 8-Hydroxychmolinlösung ausgefällt. Mit dem Niederschlag werden die Kohlenstoffelektroden gefüllt und die durch Gleichstrombogen erregten Spektren mit einem Spektrographen mittlerer Dispersion aufgenommen.     

Search for heavy neutral leptons in e+e− annihilations at 29 GeV

A search was made in 29 GeV e⁺e^? annihilations for heavy, neutral leptons decaying to e^±X^?(ν), where X is a muon or charged meson. Six events with isolated e^±X^? pairs were found for an intergrated luminosity of 106 pb^?1. The expected background is 5.5 ± 2.2 events. Limits on $\text{σ}\text{s}\text{?}\text{B}$ depend on mass and range from 8 to 20 × 10^?5 nb.     

Enhancement of the electrochemical reduction of oxygen at platinum by nickel underpotential deposition

Polycrystalline Pt electrode was modified by underpotential deposition (upd) of nickel. The modification was performed by potential cycling in phosphate buffer pH 7. 0 containing NiSO₄, in which hydrogen and nickel upd processes were well separated. The maximum Ni upd coverage was found to be 0.3. Oxygen reduction was studied at bare and nickel upd-modified Pt. It was found that the reaction rate increased with increasing Ni upd coverage. At θ(Ni)=0.3, the current density was a factor of 2 higher compared to bare Pt (at the potential of 0.85 V). The capacitance of the electrode interface was determined in potential-relaxation experiments following interruption of the polarization current. It was found that the pseudocapacitance owing to a coverage by the adsorbed reaction intermediates was higher on the Ni-modified Pt surface than on bare Pt, which resulted in higher reaction rate. The influence of Ni adatoms on the surface coverage by the reaction intermediates was attributed to the inhibition of OH adsorption on Pt by OH ligands attached on neighboring Ni atoms.     

Le pouvoir résolvant du système „objectif-émulsion“

Sans résumé

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